The inspection of tubular workpieces is demanding because, among other things, a sufficient and interference-free coupling of the ultrasound inspection device is rather difficult. Moreover, the intensity of the received signals is very much dependent upon the surface geometry, which is the reason why a test probe is actually proposed in DE 27 40 106 which determines the alignment of two other, outer test probes in accordance with the surface geometry of the workpiece to be inspected, by means of a sound attenuation measurement. This device and the underlying method are complex and cost-intensive.
An inspection device for non-destructive inspection is known from DE 27 51 810, in which a total of six test probes, the sound beams of which intersect in a single point, are arranged in an inspecting spider. The sound-transmitting coupling is carried out by supplying water into the plane of contact. It is a drawback of this arrangement that the coupling medium is supplied in an uncontrolled manner; the effort for monitoring the coupling is thus very high.
EP 0 472 252 B1 describes an inspection device in which a chamber that is filled with a fluid and is disposed between a transducer unit and the workpiece is provided. The central fluid-conducting channel of the chamber is subdivided into several separate channels, with the number of the channels corresponding to the number of the test probes used. Basically, such a test probe works relatively well; however, increased turbulence in the fluid, and thus, frequently, the formation of bubbles, occur because of the plurality of the channels.
In a so-called cluster GEIT, only relatively small water exit openings are provided, which in turn leads to relatively small sound exit openings. Thus, only a limited or specially arranged number of test probes is possible.
In order to cause the chamber of a cluster to be filled with the fluid as quickly and completely as possible, a film, which makes the chamber smaller, so to speak, can be disposed between the transducer unit and the workpiece. In principle, though it is thus possible to fill the chamber more quickly, filling the coupling gap without any air bubbles can nevertheless hardly be realized. In addition, the film will increasingly become soiled, thus causing an ever increasing sound attenuation. Besides, such films can also cause false echoes.